default templates should allow to reference existing templates
### Release notes Improvement: reference existing templates for defining a default template ### Problem to solve Current used version: GitLab Enterprise Edition 15.2.2-ee A company defines several merge request templates to use in a shared repository. This repository is configured as "template repository" on a group level (Group > Settings > General > Templates). When a new merge request is created the user could choose of one of the stored templates. But the user always HAS to choose one. With default templates (Project > Settings > General > Merge requests > Default description template for merge requests | alternative default.md) you could define a default template to use. But you have to copy the content here. ### Intended users * repository administrator * developer who creates a merge request, issue (wherelse default templates are used) ### User experience goal Developer could create a merge request without extra need to select a template. Repository does not have to copy the default templates content to every project and therefore has DRY. ### Proposal Provide a way to _reference_ an existing template. ### Further details nothing extra ### Permissions and Security unknown ### Documentation ### Availability & Testing ### Available Tier all tiers which provide default templates ### Feature Usage Metrics The new reference implies a new field. Setting this field could be measured. ### What does success look like, and how can we measure that? The setting of the 'old' field with default template _content_ could also be measured, so you could see how many templates are migrated. ### What is the type of buyer? ### Is this a cross-stage feature? ### What is the competitive advantage or differentiation for this feature? Use DRY in configuration. ### Links / references
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